MCP (Metacarpophalangeal) Dislocation

By admin On Oct 6, 2023

Ovid: 5-Minute Sports Medicine Consult, The

Jessica Stumbo

Basics

The metacarpophalangeal (MCP) joints are relatively stable joints, especially in flexion.
Stability is provided by collateral ligaments on either side of the joint and the volar plate. The collateral ligaments are lax in extension and taut in flexion. The volar plate has a firm distal attachment to the proximal phalanx and a less stable proximal attachment to the metacarpal. It is the proximal attachment that is disrupted in a dislocation (1,2,3).
The index finger, thumb, and 5th finger are most vulnerable to dislocations.

Description

An MCP joint dislocation involves dislocation of the proximal phalanx in relation to the distal metacarpal.
Requires disruption of stabilizing structures
Dislocations may occur dorsally (most common), laterally (uncommon), or volarly (rare).
The typical mechanism for a dorsal dislocation is hyperextension at the MCP joint. With hyperextension, there is rupture of the volar plate from its proximal attachment, and due to the anatomy of the joint, there is also proximal dorsal translocation of the base of the proximal phalanx over the distal metacarpal (3).
Classification of dislocations: (3)
- Simple dorsal: Articular surfaces are in partial contact, and there is no soft tissue interposed in the joint.
- Complex dorsal: The volar plate or other tissue is interposed between articular surfaces and is, by definition, an irreducible dislocation.
- Lateral: Results from an injury to the collateral ligament, either ulnar (UCL) or radial collateral ligament (RCL). The collateral ligaments of the thumb are more commonly injured than the collateral ligaments of the fingers (4).
- Volar: Rare, but may result from severe or repetitive blows to knuckle, leading to rupture of dorsal capsule with subsequent volar displacement of the proximal phalanx

Epidemiology

MCP dislocations are much less common than proximal interphalangeal dislocations because of support from surrounding structures and protected position (2,3).
Usually occurs in index finger, thumb, or 5th finger.
Nearly always a single digit, but multiple digits may be involved.

Risk Factors

Contact and ball-handling sports
Prior history of injury or dislocation

Diagnosis

History

Will complain of pain, loss of function, and usually an obvious deformity
Dorsal dislocation generally results from forced hyperextension of digit, as in striking the heel of an opponent while diving to make a tackle, or a fall on an outstretched hand (1,3,5)[C].
Lateral dislocation is caused by an ulnarly or radially directed blow to the MCP joint, usually while in a flexed position (3,5)[C].
Volar dislocation may be seen with punching in boxing and martial arts.

Physical Exam

Evaluate and document neurovascular status before and after reduction attempts.
With dorsal dislocations, the metacarpal head is volarly displaced and will be easily palpable in the palm (1)[C].
Simple dorsal: There is obvious deformity, with the phalanx resting at 60–90 degrees of hyperextension over the head of the metacarpal (2)[C].
Complex dorsal: Much more subtle deformity, with only slight hyperextension (10–15 degrees) of the phalanx; may find dimpling or puckering of the palmar aspect of the finger where the volar plate is caught between the ends of the bones (proximal phalanx and head of metacarpal). This is pathognomonic for a complex dislocation; slight ulnar deviation of the involved digit also may be noted (1,2,6)[C].
Lateral: Swelling and tenderness along the ulnar or radial side of the MCP joint; assess for injury and laxity of the collateral ligaments by stressing the ligament with the MCP joint in flexion (4,5)[C].
Volar: Obvious deformity, with the phalanx positioned palmar to metacarpal

Diagnostic Tests & Interpretation

Imaging

Anteroposterior (AP), lateral, and oblique views of involved digit (not the entire hand) generally show deformity, joint space widening, and any accompanying fracture.
Brewerton view (MCP joint flexed to 65 degrees, with the dorsum of the proximal phalanx flat against the film cassette and the beam angled 15 degrees ulnar to radial) helpful in identifying collateral ligament avulsion fractures and fractures of the metacarpal head (2,3,4)[C]
Presence of a sesamoid in the widened joint space of the involved digit is pathognomonic for a complex dorsal dislocation (because sesamoids are embedded in the volar plate) (1,2)[C].
In skeletally immature patients, it is important to image the contralateral side in order to adequately evaluate for growth plate injuries.
In skeletally mature patients, stress radiographs are sometimes utilized. Stress x-rays should only be done after static x-rays to prevent nondisplaced fractures from becoming displaced fractures. In the thumb, MCP joint laxity >30–35 degrees on stress x-rays is usually associated with a complete collateral ligament tear. Stress x-rays are not typically utilized in the skeletally immature patient because those patients are more likely to have a growth plate injury.
Postreduction views: AP, lateral, and oblique to evaluate for joint congruity and/or fracture
Up to 50% of MCP joint dislocations may have a concomitant fracture of the proximal phalanx base and/or the metacarpal head.

Differential Diagnosis

Fracture of phalanx or metacarpal
Tendon rupture
Disruption of volar plate

Treatment

Various methods of anesthesia can be utilized for reduction, including local intra-articular, regional block, or IV sedation. Typically for intra-articular injections, a short-acting local anesthetic such as 1% lidocaine without epinephrine is used, although a longer-acting agent such as bupivacaine may also be used. It is important to document neurovascular status prior to the administration of the anesthetic agent.
Usually not necessary for simple dislocations, but intra-articular anesthesia or wrist block may facilitate reduction and prevent false conclusion that dislocation is complex if patient prevents reduction due to pain.
For complex dislocations, digital block or general anesthesia in the operating room may be necessary if closed reduction is to be attempted.
Document neurovascular status before and after reduction.
In general, reduction of dorsal MCP dislocations differs from most other dislocations in that distal traction should be avoided. By using traction, a simple dislocation can be converted to a complex one because the volar plate gets displaced and locked within the joint space (1,6)[C].
Simple dorsal: 1st, relax flexors by placing wrist and IP joints into flexion; next, accentuate dislocation slightly by hyperextending proximal phalanx to 90 degrees (controversial), and then push base of proximal phalanx distally over the articular surface of the metacarpal into flexion while maintaining contact with metacarpal head to prevent entrapment of the volar plate (thus converting a simple dislocation into a complex one) (5,6)[C].

P.375

Complex dorsal: Attempt at closed reduction is warranted, but usually not successful; reduction technique is similar to that of a simple dislocation (2)[C].
Lateral: Closed reduction is usually accomplished with gentle longitudinal traction, taking care not to interpose any soft tissue.
Volar: Generally is performed open because concomitant dorsal hood injury needs repair.
Reasons for failed closed reductions: Volar plate is interposed in the joint space or metacarpal head has buttonholed through the palmar structures (1)[C]
Evaluate and document neurovascular status post reduction.
Evaluate tendon and ligament function. With thumb MCP dislocations, it is very important to assess the integrity and stability of the UCL.
AP, lateral, and oblique radiographs of the involved digit to evaluate for joint congruity and/or fracture
Simple dorsal: Dorsal blocking splint to prevent extension beyond neutral with the MCP joint in 50–70 degrees of flexion for 7–10 days if no evidence of significant instability; buddy taping also may be implemented. Active flexion exercises are permitted. With thumb MCP dislocations, a thumb spica splint is used for immobilization (1,2)[C].
Complex dorsal: Postoperative immobilization is at the prerogative of the surgeon (ranges from buddy taping for 4–6 wks to immobilization in 60 degrees of flexion).
Lateral: Majority of complete ligamentous injuries are splinted in 30–50 degrees of MCP flexion for 2–4 wks followed by buddy taping; with significant instability especially of the border digits, primary surgical repair of the collateral ligament may be considered. Incomplete MCP collateral ligament injuries and complete tears in nonborder digits are usually treated with buddy taping and early range of motion exercises (2,4,5)[C].
Volar: Postoperative management varies and is at the prerogative of the surgeon.

Medication

NSAIDs for pain relief and to decrease inflammation.
If surgery is planned, may consider acetaminophen to avoid potential bleeding risks.

Additional Treatment

General Measures

PRICE: Protection, Rest, Ice, Compression, Elevation

Additional Therapies

In dislocations of the thumb, assessment of the UCL is essential. With a hyperextension/hyperabduction injury, a Stener lesion can result. A Stener lesion occurs when the adductor aponeurosis becomes interposed between the torn end of the UCL and its bony attachment on the proximal phalanx. Spontaneous healing cannot occur since the ligament is no longer in contact with its bony attachment (7).
Occupational therapy may be indicated in more severe injuries.
Dorsal dislocations that are stable post-reduction need to be placed in a dorsal extension blocking splint to prevent extension beyond neutral and hyperextension. This position allows the volar plate to heal. Time frame is variable but typically 2–3 wks. While in the extension blocking splint, active range of motion (ROM) is encouraged to prevent joint stiffness.
Thumb MCP dislocations require immobilization in a forearm-based thumb spica splint or cast for 4–6 wks.
Initial therapy will focus on control of pain and swelling. General progression through rehab includes regaining full active ROM, followed by strengthening, and then function (activities of daily living and work-/sport-specific functions).
If the injury can be properly protected in a splint or cast, an athlete may be able to return to activities immediately. Otherwise, after the injury has healed (3–6 wks), an athlete can return to play with buddy taping for 1–3 more wks for additional protection.

Surgery/Other Procedures

Surgery is often necessary for reduction, specifically for the complex dorsal and volar dislocations, as discussed above, and may be indicated for repair of severely damaged structures in other forms of dislocation (ie, complete tear of UCL or RCL in lateral MCP joint dislocation).

Ongoing Care

Follow-Up Recommendations

After successful closed reduction, most MCP dislocations should be followed up with an orthopedic surgeon or hand surgeon within a week.

Patient Education

Warn patients that finger and hand swelling can take months to resolve.

Prognosis

Prognosis of most MCP dislocations is good as long as identified early and managed appropriately.

Complications

Joint stiffness and/or flexion contracture
Degenerative/post-traumatic arthritis
Avascular necrosis
Osteochondral fracture
Tendon adhesions/stiffness
Ligamentous laxity
Damage to the neurovascular bundle during open reduction
Premature closure of the physeal plate (rare) (1,3)

References

1. Dinh P, Franklin A, Hutchinson B, et al. Metacarpophalangeal joint dislocation. J Am Acad Orthop Surg. 2009;17:318–324.

2. Ashkenaze DM, Ruby LK. Metacarpal fractures and dislocations. Orthop Clin North Am. 1992;23:19–33.

3. Hubbard LF. Metacarpophalangeal dislocations. Hand Clin. 1988;4:39–44.

4. Lourie GM, Gaston RG, Freeland AE. Collateral ligament injuries of the metacarpophalangeal joints of the fingers. Hand Clin. 2006;22:357–364, viii.

5. Lee SJ, Montgomery K. Athletic hand injuries. Orthop Clin North Am. 2002;33:547–554.

6. Wolov RB. Complex dislocations of the metacar-pophalangeal joints. Orthop Rev. 1988;17:770–775.

7. Miller RJ. Dislocations and fracture dislocations of the metacarpophalangeal joint of the thumb. Hand Clin. 1988;4:45–65.

Additional Reading

Palmer RE. Joint injuries of the hand in athletes. Clin Sports Med. 1998;17:513–531.

Rettig AC. Athletic injuries of the wrist and hand: part II: overuse injuries of the wrist and traumatic injuries to the hand. Am J Sports Med. 2004;32:262–273.